Social insects put the ‘I’ in team to fight disease

Associate professor Rebeca Rosengaus studies the immune systems of social insect species like ants and termites. Photo via Thinkstock.

Social insects such as ants, ter­mites, and some bees and wasps live in a sort of eternal “air­plane envi­ron­ment,” according Rebeca Rosen­gaus, an asso­ciate pro­fessor in Northeastern’s Depart­ment of Marine and Envi­ron­mental Sci­ences. That is, they live in con­fined quar­ters, sharing the same air, food, and even microbes for their entire lives.

Like jet­set­ters, she said, “social insects are exposed to pathogens just like every­body else in the world, but have the added hand­icap of being social.”

Fol­lowing the air­plane analogy, one might sus­pect that sociality would increase the risk of infec­tion, as microbes readily pass from one indi­vidual to the other. But, in fact, Rosen­gaus’ work has shown the exact oppo­site: social insects deal with dis­ease much better when they’re in groups than when they’re isolated.

In pre­vious research, Rosen­gaus’ team showed that the so-​​called “social stomach” of indi­vidual ants, which pro­duces droplets of liquid food to be passed from one adult ant’s mouth to the next, doesn’t just ensure the delivery of nutri­ents to the entire group. It also pro­motes the transfer of immune pro­teins from immu­nized to non-​​immunized mem­bers of the colony.

Rebeca Rosen­gaus is an asso­ciate pro­fessor in the Depart­ment of Marine and Envi­ron­mental Sci­ences. Photo by Brooks Canaday.

In a paper pub­lished in the journal Biology Let­ters, Rosen­gaus’ team has expanded that research to include an exam­i­na­tion of ant larvae. Given the metic­u­lous grooming that ant larvae receive from workers, as well as the transfer of fluids from the workers’ “social stom­achs” to the larvae, Rosen­gaus hypoth­e­sized that the imma­ture larvae may receive less nat­ural immu­ni­ties and instead focus their energy on growing faster.

“It’s costly to pro­duce immune pro­teins, because it takes energy away from you,” Rosen­gaus said. “If you’re a little larva that wants to grow fast and get plump, why should you pro­duce your own immune pro­teins if you’re get­ting the immune goodies from some­body else?”

Rosen­gaus explained that if social transfer of immune pro­tec­tion via mouth-​​to-​​mouth regur­gi­ta­tion were enough, then evo­lu­tion should have reduced the work young ant larvae put into building their own immu­nity. To test this, her team vac­ci­nated larvae by injecting them with killed bac­teria (the same way humans are vac­ci­nated) or a saline solu­tion and then placed them with workers who tended to the larvae. On the third day, the team exposed the larvae to live, more destruc­tive bac­teria. They found that the vac­ci­nated insects were five times more likely to sur­vive the chal­lenge than those unvaccinated.

This con­firmed that ant larvae have retained their indi­vidual immune sys­tems throughout mil­lions of years of evo­lu­tion despite the fact that workers pro­vide exten­sive brood care, Rosen­gaus said, and that imma­ture larvae are indeed capable of immune priming.

The find­ings point to yet another method by which social insects deal with dis­ease. In the age of phe­nomena such as colony col­lapse dis­order among bees and inva­sive fire ant pop­u­la­tions in the southern United States, under­standing the mul­tiple mech­a­nisms of social insect immu­nity is crit­ical, according to Rosengaus.

“We’re trying to under­stand the inter­ac­tion between group living and immu­nity at the dif­ferent levels of bio­log­ical com­plexity, from the mol­e­cules, to the pro­teins, to the indi­vidual, to the group, to the society,” she explained. “At every step as you go up the hier­archy of com­plexity, you could expect dif­ferent emer­gent prop­er­ties of an immune system.”

This new research shows that ant larvae can gen­erate an immune response. This indi­vidual capa­bility, together with the social trans­mis­sion of immune func­tion via mouth-​​to-​​mouth regur­gi­ta­tion from workers, helps the entire colony sur­vive path­o­genic challenges.

Inter­est­ingly, Rosen­gaus believes that the social nature of the insects, and the ability to transfer immune pro­teins from one ant to another, may have shaped the phys­ical attrib­utes of the immune pro­teins them­selves. Immune pro­teins, to be effec­tive when shared among nest­mates, need to be robust. They should not degrade easily during the exchanges and should retain antimi­cro­bial activity during and after their transfer. She said the ability to gen­erate immu­nity at the indi­vidual level and the exchange of immune pro­tec­tion between indi­vid­uals in a colony may be one reason why social insects are so geo­graph­i­cally wide­spread and so eco­log­i­cally dominant.

About the Writer

Angela Herring is the science writer for the Northeastern news team. In a past life, she made fullerenes (aka bucky balls) at a small chemical company outside of Boston while freelance writing for the Harvard Stem Cell Institute, the Broad Institute and Novartis Biomedical Research Institutes. She earned her Bachelor's degree in chemistry and literature from Bennington College in 2005. In addition to writing stories for the News@Northeastern, she also maintains the university's research blog: iNSolution.

News@Northeastern is Northeastern University’s primary source of news and information. Whether it happens in the classroom, in a laboratory, or on another continent, we bring you timely stories about every aspect of life, learning and discovery at Northeastern. Contact the news team